DE2539764A1 - METHOD OF COATING A HEAT-RESISTANT CARRIER MATERIAL WITH AN ACTIVE METAL OXIDE FILM - Google Patents

Description

DIPL.-ING. H. STEHMANN ZEXSIL · ** -.

DIPL.-PHYS. DR. K. SCHWEINZER TEL .: OFFICE 0 * 1.205727 PRIVATE: 374504

. DR. M. RAU

TB 2 S 3 ^ 7 B Λ ΙΑΝΚΚΟΝΤΕΝ:

ί. <J ■>) \ J f U * t DEUTSCHE BANK

DEUTSCHE BANK AG. NOBNiERO BlZ 7 * 070012 ACCOUNT NO. S41144 • CHECK ACCOUNT: NOtNtEKe

Nuremberg, September 5, 1975 1720/38

Air Products and Chemicals Inc., Allentown, Pennsylvania / USA

"Process for coating a heat-resistant carrier material with an active metal oxide film "

The invention relates to a method for coating a heat-resistant carrier material with an active metal oxide film.

The support material is the base material of a catalyst as its lower or inner zone in Form of a heat-resistant monolithic structure covered with a film of catalytically active heat-resistant metal oxide is to be coated. In particular, this invention relates to providing such a coating that which is firmly adhered to the heat-resistant base structure and has a substantially uniform thickness.

Stable, one-piece or homogeneous structures of the so-called "knitted" type, often called monolithic structures or called monoliths, have wide application in the manufacture of catalysts for conversion of exhaust gases containing flammable impurities. The reason lies in the compactness and

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For da * Ordinance VerhHnls gll «dl · Schedule of fees of the German Chamber of Patent Attorneys. - Place of jurisdiction for performance and payment: Telephone calls have no legally binding effect

multiple manageability and interchangeability of such monoliths. These generally indicate a large number Channels or passages for the exhaust gases. An inorganic oxide is used as a thin surface film on the Inner zone in the form of the heat-resistant basic structure. The monolith thus coated becomes ordinary impregnated with a catalytically active metal, such as a metal from the platinum group. The resulting The catalyst can then be placed in a suitable container for the conversion of exhaust gases.

The invention is based on the knowledge that it often causes difficulties, the monolithic structures to be coated with the surface oxide. The main difficulty encountered in practice is to find a Coating with surface oxide to create that is uniform and does not have any of the channels or passages of the Clogged monoliths. In particular, it is the non-uniformity of the coating film that in practice causes clogging the channels leads. This in turn leads to a reduction in the effectiveness of the catalyst and at the same time to an increase in the pressure drop across the container in which this catalyst is used.

The object of the invention is accordingly to provide a method for preparing the catalyst support material, that into a uniformly distributed, smooth and firmly adherent Coating with an active metal oxide film, which is deposited on the monolith without the previously observed problems of clogging of passages occur in the case of conventionally applied Procedures for preparing such monoliths occurred.

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This object is essentially achieved according to the invention solved the sequence of the following procedural steps:

a) a monolithic basic structure (monolith) is converted into a Immersed suspension of active metal oxide;

b) the monolith is removed from the suspension again;

c) the monolith soaked with suspension is spun for so long, until essentially all of the excess suspension is removed and only a film of active metal oxide remains of substantially uniform thickness; and

d) this remaining coated monolith is kept at a temperature in the range between about 400 C (750 ° F) and roasted 980 ° C (1800 ° F).

A preferred example of a monolith of the type considered here, as it is intended for treatment according to the method according to the invention, consists of an essentially continuous web of a ceramic material such as in particular alpha-alumina (alpha-aluminum oxide), sillimanite, petalite, cordierite ( Dichroic), (2MgO · 2Al ₂ O ₃ SSiO ₂ ), mullite, (3Al 0--2SiO ₂ ), zircon, zircon-mullite, spodumene, magnesium-silicates (magnesium-silicic acid compounds), alumino-silicates and the like. The web of the material used in each case is wrapped crosswise in the manner of a herringbone pattern in order to form a cylinder which has a longitudinal central cavity and a system of unevenly distributed through-channels. The diameter of each such channel should be at least about 0.5 mm in order to ensure that the suspension can pass through here during the process step of centrifuging the previously immersed monolith.

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Another type of monolithic structure that is also suitable for use in the present invention is, consists of an extrusion or a plate stack of ceramic material, which a variety having adjoining, mutually parallel and in the same direction extending passage channels. Monoliths designed in this way are generally referred to as honeycomb monoliths.

Because all axes of the passage channels in such honeycomb monoliths extend in the longitudinal direction, such monoliths must be thrown with such a direction of rotation be that the axis of rotation is perpendicular to the axis of the channels.

For the active metal oxides involved in practicing the invention If the process is expediently used, surface materials such as alumina (aluminum oxide) , Silica, zirconia, alumina-silica, alumina-zirconia and the like can be considered. Preferably Alumina is used as the active metal oxide, which is placed on the monolithic support of the catalyst in the form of a suspension applied and then converted into gamma-alumina during the final roasting process step will.

The alumina suspension is expediently formed in that an excess of aluminum metal with a Acid is added, which is selected from the group of acids, to which HCl, HBr and HI belong, or with a Aluminum salt such as aluminum chloride, bromide or iodide, until hydrogen no longer evolves. The resulting Suspension, the Hydro-Sol, is white and transparent

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like water, in contrast to the gelatinous suspension of discrete particles of alumina. A detailed description the preparation of a suspension suitable for carrying out the method according to the invention can be found in U.S. Patent 3,346,336.

Following the process step of immersing the Monolith in the suspension to wet all channels contained in the monolith, the monolith with a centrifugal acceleration of at least 2 g centrifuged until all excess suspension is thrown off is, only a uniform, smooth and firmly adhering coating of the suspension remains. These The spin period generally lasts between one and thirty seconds.

The final step in the process is roasting from heating the coated monolith at temperatures on the order of about 400 ° C (750 ° F) to 980 ° C (1800 ° F), preferably in the range between about 540 ° C (1000 ° F) and 870 ° C (1600 ° F), for 0.5 to 5 hours.

Further features and advantages of the invention emerge from the following description of a shown in the drawing preferred embodiment for devices for practicing the method according to the invention. It shows:

Fig. 1 is an end view of a device for practicing the method according to the invention during the Diving, and

FIG. 2 is a side view of the device according to FIG. 1 during spinning.

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In the illustrated device, a trough 10 is present, of which only part of its volume of one Alumina suspension or slurry 11 is ingested. Monoliths 12 of the leg honeycomb type are in pockets or Cups 14 are used, which have a large number of perforations or openings 15. The four cups 14 of the illustration of the drawing form a group in that each of these cups 14 is fixedly connected to one end of a rod 16 is. The other end of each of these rods 16 is attached to a mandrel 18. In the practical execution In such devices, a plurality of such groups of cups 14 are arranged next to one another along the dome 18 (not shown in the drawing). A bracket 2 0 cooperates with claws 22 on a respective cup 14 in such a way that the monolith 12 inserted into cup 14 during the dipping and spinning process steps therein is being held. The bracket 2 0 is expediently inserted into the claws 22 that the coated Monolith 12 easily out of cup 14 upon completion of the process step taken out of the spinning and replaced by another monolith 12, which is coated in the same way can be replaced. The bracket 20 has contact with the latter only on the outer circumference of the monolith 12 so that the suspension 11 can easily enter all of the channels 23 when the monolith 12 is immersed in the suspension 11 is, and then during the process step of spinning the excess suspension 11 from this again can emerge.

During the immersion, the mandrel 18 is driven by a drive 26

slowly rotated (process step shown in Fig. 1), so that one after the other each of the clamped monoliths 12 is immersed in the suspension 11, around the channels 2 3 completely

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to wet. After so all the monoliths 12 are immersed were, the mandrel 18 is raised vertically to the position shown in Fig. 2, including any device according to the state of the art (not shown in the drawing) can be used. The wetted monoliths 12 are then at a centrifugal acceleration of about 2 to 10 g, based on the center of mass of each monolith 12, 5 to 30 sec. long spun to remove excess suspension from them. After that the coated Monoliths 12 are removed from their cups 14 and at temperatures between about 540 ° C (1000 ° F) and about 815 ° C (1500 ° F) roasted to convert the alumina suspension to gamma-alumina. This will match the one in the drawing shown device for practicing the method according to the invention an optimal efficiency with regard to the coating such monoliths 12 obtained with a uniform film of alumina sol, the thickness of which is preferably in the Is on the order of about 0.102 to 0.0254 mm (0.004 to about 0.001 inches).

The monoliths coated with alumina according to this invention are particularly suitable for use as one-piece Catalysts in catalytic converters for automobile exhaust gases. Such ietalysatoren contain the coated Monolith together with one or more catalytically active metallic components, which are preferably from group VIII of the periodic table of the elements and are precious metals like platinum, palladium and rhodium. Others suitable for this Components include one or more of the oxides of copper, iron, nickel, cobalt, chromium, manganese, tin, Vanadium, tungsten, molybdenum, silver, gold, germanium or the like. To the patent application "Method for impregnating a block-shaped Basic structure coated with an active metal oxide is, with a catalytic metal and devices for practicing the method "from the same day of the applicant Reference is made in full.

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The more catalytic! Components can be based on the Alumina coated monoliths can also be applied by conventional methods, generally from immersion of the Monoliths in an aqueous solution of a mixture of the desired metallic components for impregnation run out of the outer surface of the alumina coating.

In the case of the use of noble metals, the carrier is treated with an aqueous solution of platinum hydrochloric acid, Platinum chloride, ammonium chloroplatinate, dinitrodiamino platinum and the like. Impregnated. The impregnated carrier is then oxidized and / or reduced to oxidize the platinum in to achieve or reduced form. The mixture of catalytic metals decomposes during roasting to form the mold of the oxide.

The amount of catalytic components will vary depending on the particular end-use application envisaged. In general the amount is about 0.05% to 10%, preferably in the range between 0.1% and 1%, based on the weight of the complete Catalyst with its carrier material.

The following examples are intended to explain in more detail the practice of the method according to the present invention, namely that Preparation of the catalyst carriers and their use as catalysts for the treatment of engine exhaust gases.

Example 1:

The monolith used in this example consisted of ceramic alpha-alumina, which became herringbone-like from a thread a ball-shaped structure, in which the individual wires crossed one another to create a

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to obtain a cylindrical shaped bundle leaving a central axial cavity. That kind of threads wound on top of one another formed passage channels, from some of which were at least approximately perpendicular to the longitudinal axis of the cavity and thus to the longitudinal axis of the monolith, so that the resulting flow of exhaust gases when a finished catalyst turns into a catalytic one Exhaust or muffler is inserted, either from the axial cavity through that nest-shaped structure radially outside or from its outside circumferential surface through this nest-like structure runs towards the central cavity.

Rubber stoppers were inserted into the two ends of the axial bore of the monolith and one shaft made of stainless steel Steel is introduced into this rubber stopper through the axial openings. This axis was in the chuck clamped in a compressed air motor from "Arrow Engineering". Alumina hydrosol was placed in a trough had a density of 1.23 g / cm and by adding one liter of hydrochloric acid to 1300 g of alumina chips plus three liters of water in a reflux condenser during 100 hours has been won. The undissolved aluminum was carried over to the next batch. The container was around the axis raised around the monolith 5 to 10 sec. completely immersed for a long time at room temperature, whereupon this container was lowered again. The monolith became with a centrifugal acceleration occurring on the cavity wall from about 2 g 10 to 20 sec. long spun until the coated monolith was almost dry to the touch. The alumina hydrosol, that now covered the monolith was evenly distributed over its entire surface. They weren't reflective white zones remained. All passage channels in the monolith were therefore open, free of clogging alumina deposits. This monolith coated in this way was then used in

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a temperature of about 120 C (250 F) and dried at 593 ° C (1100 ° P) in air in a muffle furnace for 2 hours roasted. This sequence of treatments was repeated six times to add 0.11 g of alumina coating per gram of bare monolith, d. H. 10 percent by weight of alumina based on the finished catalyst support.

The roast temperature of 593 ° C (1100 ° F) for the coated Monoliths after each immersion process were found to be sufficient to adequately fix the alumina sol on the monolith and to drive off a sufficient amount of hydrochloric acid so that the coating of gamma-alumina during of the next dipping process did not soften. However, the grate temperature dropped to around 790 C after the last dip (1450 ° F) to reduce the chloride ion content of the finished catalyst, and thus its To maximize activity.

The catalyst carrier treated in this way was subjected to a test in an ultrasonic bath to determine the adhesiveness of the active alumina coating. The results are compiled in Table I below and are for assessment juxtaposed with a mere monolith. That for

The ultrasonic bath used in this text was an Ultrasonic Water TM
tank of the type "Megason", as it is traditionally used for

Cleaning surgical instruments.

Example 2:

The treatment sequence according to Example 1 was again carried out, with the exception that the density of the alumina sol which was used for the immersion process step was now 1.41 c / cm . The treatment was repeated three times to deposit 0.1 g of alumina per gram of the bare monolith.

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The carrier treated in this way was also tested in an ultrasonic bath, and these results were also tested are compiled in Table I below.

Example 3;

Compared to the procedure according to Example 1, an alumina sol with a density of 1.4-3 g / cm was now used for dipping and the treatment was repeated only twice to achieve the same proportion of alumina on the monolith.

The results of the ultrasonic bath test are also for this monolith given in Table I below.

... Table I.

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- 12 Table I.

Adhesion of the alumina coating, tested in an ultrasonic bath example

Number of dives in the sol

Grams of coating per gram of bare monolith Weight before the ultrasonic bath (g) Weight after the ultrasonic bath (g) Weight loss (g)
Weight of the grit in the container (g)

Weight of the grus in relation to the monolith (%)

Coating loss if the grit consists only of coating (%)

control 1 2 3 O 6th 3 2 O 0.11 0.10 0.10 397.13 438.46 460.38 453.32 396.95 438.50 460.22 452.95 0.18 0.04 (profit) 0.16 0.37 0.14 0.12 0.16 0.22 0.035 0.027 0.034 0.048

0.25

0.35

0.49

253976A

The results in Table I show that the active alumina is tenaciously retained on the alpha-alumina monolith.

Examples 4 to 6:

Each of the finished treated catalyst carriers, as described in Examples 1 to 3, was impregnated in such a way that it was provided with a total of 0.778 g of platinum and palladium at a platinum / palladium ratio of 5/2. The results of test pieces cut from the catalysts described above and tested in an engine laboratory at an exhaust gas velocity of 15,000 GHSV (that is the velocity of a unit volume of gas based on the volume of the catalyst, measured in hours) are shown in Table II below summarized. After being tested in the fresh state, these test pieces were subjected to a standard aging process, namely 24 hours at about 980 C (1800 F), and then tested again. The results achieved therewith are also shown in Table II below. The test results denote the temperatures at which 50% (or 80%) of the carbon monoxide (CO) in the feed gas (exhaust gas) is converted into carbon dioxide, respectively. the hydrocarbons (HC) has been converted to CO ₂ and H ₂ O; For the temperature data, the original measurement results in ° F are inserted in Table II, the corresponding temperature data in ° C results from the relationship ⁰ C = (5/9) (F - 32).

A catalyst produced according to the invention is therefore characterized by high activity, also in comparison with other catalysts for the treatment of motor vehicle engine exhaust gases, with the low temperatures at which the conversions in a given Measurements take place, are a benchmark for the activity of the catalysts.

... Table II - 14 -

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292 274 274 306 281 279 300 277 278 314 285 283

Table II Test of the catalysts in an engine laboratory at 15,000 GHSV

Example 4_ 5_

Monolith of the early 12th century

Example

Fresh catalysts,
Test conditions in
Engines laboratory

T ₅₀ CC ⁰ FT ₅₀ HC ⁰ F T ₈₀ CO, ° FT ₈₀ HC ⁰ F

After 24 hours of aging at ca.980 ⁰ C (1800 ⁰ F)

T ₅₀ CC ⁰ FT ₅₀ HC ⁰ F

^T80 CC ° F

Tg ₀ HC ⁰ F 425 410 400

Example 7:

A dichroic ceramic honeycomb structure was used for this example. Such basic structures are brought into trade by the company Corning Glass Works. The dimensions were 4.5 inches (11.5 cm) in diameter and 3 inches (7.6 cm)
Length, and the monolith had 15 square passageways per inch. This honeycomb monolith was in a hydro-sol with a density of 1.38 g / cm for about 5 to 10 seconds. immersed for a long time to completely moisten its passageways.

385 375 380 385 382 386 400 385 395

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The monolith was then removed from the hydro-sol again and attached to the shaft according to Example 1 so that the axes of the channels are perpendicular to the Rotating shaft were aligned; the spinning then took place in such a way that a centrifugal acceleration of am Inner radius about 2 g 10 to 20 sec. long occurred until the Hydro-Sol coating on the monolith was no longer tacky was. The honeycomb monolith so coated was then toasted at 593 ° C (1100 ° F) for two hours. The above The treatment sequence described was repeated a second time to add 0.15 g of alumina coating per gram of the bare To apply monoliths to the basic structure. Practically all of the nearly 3,600 square openings in the honeycomb monolith were then open, i.e. free from clogging deposits.

The method according to the present invention has the particular Advantage of a film made of Alumina-Hydro-Sol, which has a density in the range of about 1.2 to 1.45 g / cm, to be able to apply uniformly to a monolithic basic structure without clogging its passage channels. The process can be repeated several times in succession in order to obtain a catalyst support which has a coating made of active gamma alumina of the strength just desired. This strength is usually in the range from 5 to 20 percent by weight.

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Claims (10)

Expectations b) the monolith is removed from the suspension again; c) the monolith soaked with suspension is spun for so long, until essentially all of the excess suspension is removed and only a film of active metal oxide remains of substantially uniform thickness; and d) this remaining coated monolith is at a temperature ranging between about 400 ° C (750 ° F) and 980 ° C (1800 ° F) roasted. 2. The method according to claim 1, characterized in that a centrifugal acceleration of at least a mean 2g acts on the monolith during spinning. 3. The method according to claim 1 or 2, characterized in that the immersion in alumina-hydro-sol takes place as the active metal oxide. 4. The method according to claim 3, characterized in that the Immerse in Alumina-Hydro-Sol with a density in the range of 3
about 1.2 to 1.45 g / cm. 5. The method according to any one of claims 1 to 4, characterized in that the sequence of process steps a) to d) is repeated until about 5 to 20 percent by weight of alumina is deposited as a coating on the monolith. 6. The method according to one or more of the preceding claims, characterized in that following this treatment of the catalyst carrier, a catalytically active metal is applied in order to create a catalyst for engine exhaust gases. 6,99816 / 0927 - 2 - 7. The method according to claim 6, characterized in that a noble metal from group VIII of the periodic table of elements is used for this aftertreatment with catalytically active metal. 8. The method according to one or more of claims 1 to 7, characterized in that the monolith immersed according to the first process step a) has a plurality of through-channels, that the roasting process step lasts for 0.5 to 5 hours, and that the sequence of the four process steps is repeated until the monolith is coated with 5 to 20 percent by weight of active alumina. 9. The method according to one or more of claims 1 to 8, characterized in that the monolith is thrown during process step c) with a centrifugal acceleration of 2 to 15 g on average. 10. The method according to one or more of claims 1 to 9, characterized in that a monolith of the honeycomb type is used, which has a plurality of parallel through-channels and is rotated about an axis during the method step of spinning runs approximately perpendicular to the axis of these through-channels. ΒΠ98 16/0927